Black Knights of the Hudson is a series of audiobooks relating the saga of the fictional MacKendrick Army family from the Civil War through World War II.

Long Gray Line is the fourth audiobook in the story of the MacKendrick Army family; who live by West Point's motto of Duty, Honor, Country. The war with Spain is over and the United States has moved beyond its continental boundaries. With new inventions on the horizon, the United States at last takes its place in the world order and the MacKendricks are quick to answer the challenge. The cousins Fitzjames and Jackson Lee MacKendrick arrive at West Point to assume their own places in West Point's fabled Corps of Cadets.

Jackson Lee, classmate of the impressive Douglas MacArthur, demonstrates a quiet competence and is marked closely for later advancement by the senior officers. Fitzjames, son of a legendary officer of the United States, barely survives the tender mercies of the Yearlings in Beast Barracks when he is hazed brutally for his effrontery in bearing such a famous name.

In Long Gray Line, the MacKendricks march forward to greet the new century and its bewildering array of inventions. From the football field of the annual Army-Navy Game, where the canny Charlie Daly leads the Cadets against the Midshipmen, into the growing clouds of a world war, Jack and Fitz assume their fathers' mantles as the next generation of West Point's famed Corps of black knights. Attractive, engaging, from a background of wealth and privilege, the MacKendrick cousins prove to be fair game to the Army brats, college girls, New York society women, and English Ladyships who seek to join the equally important line of Army wives who have taken Milton's words as their own motto: 'they also serve who only stand and wait.'